This invention relates to a hologram duplicating apparatus and a hologram duplicating method for duplicating hologram in which a holographic stereogram is used as the original, a hologram producing apparatus and a hologram producing method for producing hologram in which a holographic stereogram is used as the original, and an intermediate hologram producing apparatus and an intermediate hologram producing method for producing intermediate hologram used for duplication or production thereof.
Holographic stereograms are produced by allowing a large number of images obtained by successively imaging object from different observation points to be original image to successively expose and record such images as rectangular or dot-shaped element holograms on a single recording medium for hologram. In the case where this holographic stereogram is observed by an eye from a certain position, two-dimensional image which is a set of image information of a portion of respective element holograms is recognized, and in the case where this holographic stereogram is observed at another position horizontally shifted from this position, two-dimensional image which is a set of image information of another portion of respective element holograms is recognized. Accordingly, in the holographic stereogram, in the case where user observes this holographic stereogram by both eyes, exposed recording image is recognized as three-dimensional image by parallax of left and right eyes.
The above-described holographic stereogram is produced by a holographic stereogram producing apparatus 100 generally shown in FIG. 1A. The holographic stereogram producing apparatus 100 is constituted by a laser light source 101 for emitting coherent laser beam L10 of single wavelength, a half mirror 102 for dividing the emitted laser beam L10 into object light L11 and reference light L12, optical components 103 to 107 and an indicator 108 which constitute optical system of the object light L11, optical components 109 to 11 which constitute optical system of the reference light L12, and an electrically operated stage 113 for holding a recording medium 112 for hologram onto which object light L11 and reference light L12 are converged, and caused to undergo traveling drive.
Specifically, the optical system of object light L11 consists of a reflection mirror 103, a first cylindrical lens 104 for magnifying object light L11 in one-dimensional direction, a collimator lens 105 for changing the magnified object light L11 into parallel light, a projection lens 106, and a second cylindrical lens 107 for conducting object light L11 to the hologram recording medium 112 of an exposure recording unit P100 which are respectively arranged from the input side thereof along the optical axis. The indicator 108 is constituted by liquid crystal panel of the transmission type, and is disposed between the collimator lens 105 and the projection lens 106. On the indicator 108, image based on image data outputted from image processing unit (not shown) is displayed.
Specifically, the optical system of the reference light L12 consists of a cylindrical lens 109 for magnifying reference light L12 in one-dimensional direction, a collimator lens 110 for changing the magnified reference light L12 into parallel light, and a reflection mirror 111 for reflecting the reference light L12 to conduct it into the hologram recording medium 112 which are respectively arranged from the input side thereof along the optical axis.
The hologram recording medium 112 is constituted by, e.g., photosensitive film, and is held by the electrically operated stage 113 as shown in FIG. 1B. When this electrically operated stage 113 is driven, the hologram recording medium 112 is caused to intermittently undergo traveling drive in the direction indicated by the arrow b in the figure.
As shown in FIG. 1A, laser beam L10 is emitted from the laser light source 101 and is incident on the half mirror 102. Thus, the laser beam is divided into object light L11 and reference light L12 by this half mirror 102.
The object light L11 is incident on the indicator 108 through the cylindrical lens 104 and the collimator lens 105, and is caused to undergo image modulation in accordance with element image displayed when the object light L11 is transmitted through this indicator 108. The image-modulated object light L11 is incident on the hologram recording medium 112 positioned at the exposure recording unit P100 through the projection lens 106 and the cylindrical lens 107. Moreover, the reference light L12 is incident on the hologram recording medium 112 positioned at the exposure recording unit P100 through the optical system of the cylindrical lens 109, the collimator lens 110 and the reflection mirror 111.
Accordingly, interference fringes produced by interference of the object light L11 which has been image-modulated by image displayed on the indicator 108 and reference light L12 are successively exposed and recorded in rectangular or dot form as element holograms on the hologram recording medium 112. In this way, holographic stereogram is produced.
Meanwhile, in ordinary hologram, illumination light source for reproducing three-dimensional image and hologram are spatially separated. For this reason, ordinarily, broad space is required for reproduction, and the positional relationship between hologram and the illumination light source must be set to the determined condition in order to carry out reproduction in the optimum condition. This is similar also in the holographic stereogram consisting of plural element holograms.
On the contrary, if the illumination light source and hologram are integrated, space for illumination becomes unnecessary so that miniaturization can be realized. In addition, since the positional relationship between hologram and the illumination light source is constant at all times, reproduction can be carried out always in optimum condition. Further, as a hologram which realizes this, there is hologram of the so-called edge lit type which allows a recording medium to be in contact with all optically transparent light introduction block to carry out recording and/or reproduction.
When a transmission type edge lit hologram in which three-dimensional image is reproduced by light transmitted through a recording medium is produced, a recording medium 121 for hologram is attached to one surface 120a of a light introduction block 120 consisting of transparent material such as glass or plastic, etc. of suitable thickness as shown in FIG. 2. At this time, ordinarily, the hologram recording medium 121 is attached to the light introduction block 120 through index matching liquid (not shown) in order to prevent total reflection of light. Further, object light 124 from object 123 is irradiated toward the hologram recording medium 121 from the other surface 120b of the light introduction block 120, and reference light 125 is irradiated toward the hologram recording medium 121 from end surface 120c of the light introduction block 120. Thus, the transmission type edge lit hologram is produced.
Further, when the transmission type edge lit hologram produced in this way is reproduced, light introduction block such as glass, etc. was attached to the hologram recording medium to allow illumination light to be incident from the end surface of that light introduction block to thereby carry out reproduction of hologram. Specifically, as shown in FIG. 3, a hologram 131 is attached to one surface 130a of a light introduction block 130 through index matching liquid (not shown) thereafter to irradiate illumination light 133 for reproduction toward the hologram 131 from end surface 130b of the light introduction block 130. At this time, light transmitted through the hologram 131 is diffracted by the hologram 131. Further, reproduction image 135 takes place by this diffracted light 134. Thus, the reproduction image 135 is observed by an observer 136.
In the above-mentioned FIG. 3, the case where incident angle of reproduction illumination light of hologram is 60 degrees was indicated as an example. By introducing reproduction illumination light 133 through the light introduction block 130 in this way, it is possible to prevent surface reflection between hologram recording material and air. Since this effect becomes conspicuous particularly according as light incident angle of reproduction illumination light 133 becomes sharp, it is considered that the edge lit hologram is advantageous in realization of compact reproducing unit.
Meanwhile, since the edge lit hologram has various merits as previously described, there is high possibility that the edge lit hologram is utilized as a general image display apparatus. In this case, it is assumed that the necessity of duplicating a large number of holograms in which the same image information is recorded in the state where image quality is maintained takes place.
Hitherto, in the case of mass-producing duplications of holograms, the so-called one step method in which an original and photosensitive material for printing duplication are exposed in the state where they are caused to be in contact with each other was used as a general technique.
As one example of the one step method, the example where image of the original is duplicated and recorded on other recording medium for hologram in which a holographic stereogram is used as the original to produce edge lit hologram is shown in FIG. 4.
As shown in FIG. 4, in carrying out duplication and recording, a recording medium 141 for hologram for duplicating and recording image of the original is first attached to one surface 140a of a light introduction block 140. Then, an original 142 is attached to the hologram recording medium 141 attached on one surface 140a of the light introduction block 140 through index matching liquid.
In the state where the original is attached in this way, reference light 143 equivalent to illumination light for reproduction of the original 142 is caused to be incident into this light introduction block 140 from end surface 140b of the light introduction block 140.
The reference light 143 incident into the light introduction block 140 is transmitted through the hologram recording medium 141 and is incident on the original 142. The incident light is totally reflected by base film (not shown) of the original 142. Further, because of that the reference light 143 totally reflected by the base film is irradiated onto hologram recording material of the original 142, image recorded on this hologram recording material is reproduced.
Reproduction light of this original 142 is incident for a second time on the hologram recording material of the hologram recording medium 141 as object light. Further, the reproduction light of the original 142 incident as object light on the hologram recording material of this hologram recording medium 141 interferes with the reference light 143 incident into the light introduction block 140 within this hologram recording material. Thus, interference fringes of the reproduction light of the original 142 and the reference light 143 are recorded on the hologram recording material of the hologram recording medium 141, and image recorded on the original 142 is duplicated and recorded on the hologram recording medium.
In a manner as described above, by the 1 step method, image of the original is duplicated and recorded on other hologram recording medium in which the holographic stereogram is used as the original. Thus, edge lit hologram is produced.
However, the above-described 1 step method is suitable for duplication of hologram of the reflection type, but was not suitable for duplication of hologram in which image quality is maintained because there take place many factors which disturb image quality including double refraction at the surface of the contact portion of the light introduction block and the hologram recording material at the type where reproduction is carried out in the state in contact with the light introduction block like edge lit hologram.
As stated above, there also exist drawbacks in the 1 step method generally used. It can be said the technology for duplicating a large number of holograms using a holographic stereogram as the original is not yet established.